1. Field of the Invention
Embodiments of the present invention relate to an inkjet apparatus that ejects and applies ink to an object using an inkjet head.
2. Description of the Related Art
An inkjet printer disclosed in U.S. Pat. No. 5,428,384 preliminarily raises the temperature of a sheet by heating the sheet from the reverse side using two heaters, thereby promoting the drying of ink applied to the sheet. The two heaters are a drive roller having a built-in preheating lamp, and a halogen lamp provided under a supporting surface in a print region.
In general, there is a time-lag from when a heater is powered on to when a predetermined amount of heat radiation is reached. If a command to drive the heater is given at the start of printing, the temperature of a part of the sheet passing during the time-lag until temperature rise is lower than desired. In the part, image unevenness such as color unevenness due to incomplete drying of ink may occur. The inkjet printer disclosed in U.S. Pat. No. 5,428,384 is provided with two heating units and preheats a sheet before printing. Providing two heaters increases power consumption and complicates the structure. The larger the printer, the more noticeable this problem.
The inkjet printer disclosed in U.S. Pat. No. 5,428,384 heats a sheet from the reverse side to dry ink droplets on the face. Such a drying method has the following problems. When the sheet used has a large thickness or is made of a highly heat-insulating material (for example, when the sheet is a resin plate or a thick vinyl sheet), it is difficult to efficiently apply heat to ink on the face of the sheet, and high-speed printing is hindered. In the case of a sheet having an adhesion layer on the reverse side thereof, such as a sheet of wall paper, the glue of the adhesion layer may be melted by heating the reverse side of the sheet. The melted glue causes a sheet conveyance jam.
On completion of printing, sheet conveyance is stopped, and the heating by the heater is also stopped. The heater continues to radiate heat due to residual heat even after being stopped. For this reason, the sheet at rest immediately below the heater continues to be heated. If the sheet surface temperature exceeds permissive temperature, the sheet may deform. This phenomenon is particularly noticeable in the case where the sheet is made of a heat-sensitive material such as plastic.